Neutralizing interfering disturbances in electric circuits



J. W. MILNOR May 21, 1929.

NEUTRALIZING INTERFERING DISTURBANCES IN ELECTRIC CIRCUITS Filed Nov. 9f 192eI 1"3--f--LT I lulllln'l Patented. May 21, 1929.

UNITED STATES JOSEPH W. MILNOR, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TOI'THE WESTERN A UNION TELEGRAPH COMPANY, OF NEW YORK, N. Y., A CORPORATION 0Fv NEW YORK. v

NEUTRALIZING INTERFERING DISTURBANCES IN ELECTRIC CIRCUITS.l

Application filed November 9, 1926. Serial No. 147,372.

This invention relates to means for neuf tralizing interference between adjacent transmission circuits,` and in particular to' means for protecting intelligence transmission circuit from disturbing influences of adjacent circuits. Y

My invention is embodied in a system in which a neutralizing current is induced 1n .an auxiliary circuit which parallels the circuits to be protected, and neutralizing voltages, equal and opposite to the disturbing voltages, are introduced into the circuits to be protected by an inductive coupling between these circuits and the auxiliary circuit.

One of the objects of my invention is to provide an improved form of transformer for coupling the auxiliary circuit to the circuits to be protected.

Another object of my invention is to provide simple and eiiicient means for adjusting the phase angle between the disturbing voltage and the neutralizing voltage to the propy er value.

Still another object of my invention is to devise a neutralizing system in which the cross-lire between adjacent circuits to be protected is reduced to a minimum. y

A further object of my invention is to provide a neutralizing system in which the detrimental effect of ground currents, or direct current, flowing in the auxiliary circuit is substantially eliminated. i

My invention is illustrated in the accompanying drawings in which Figure l is a diagrammatic showing of the neutralizing transformer and its circuit con` nections.

Figure 2 shows the manner of arranging the primary and secondary coils upon the transformer core and other details of the transformer construction.

Figure 3 is an equivalent circuit diagram useful in explaining the invention.

In the drawing, l, 2, 3 and 4c represent four communication wires which are to bey protected against inductive disturbances caused by an adjacent transmission circuit carrying disturbing currents. VThe disturbing circuit PATENT OFFICE.

exposure is shown extending between points A and B. rIhis. circuit maybe a power line carrying alternating current or a telegraph line, or any othercircuit carrying varying or alternating` currents.

.Theneutralizing transformer is indicated at T, the primary windings of ywhich are connected in parallel in the auxiliary circuit and a secondary coil is lconnected in each of the communication wires. Single coils may be used for communication circuits consisting of a single wire, while coils consisting' of a plurality of windings, suitably associated, may be used for communication in circuits consisting of a. plurality of wires, such as a telephone pair or phantom. The auxiliary circuit consists of a very low resistance wire D extending throughout the length of the disturbing circuit exposure A-B and is .provided at each end with low resistance ground connections E and E. The wire Dis arranged in close proximity to the communication wires and in such manner that it has inv yduced therein disturbing currents similar to those induced in the communication wires.`

desired, condensers may be used across the secondary windings of the transformer, and telephonie transmission over the communicationk wires will be somewhat improved due to the by-pass afforded by the condensers to telephone currents. l j

The conditions necessary for proper neutralization are as follows The fundamental ,requirement is that the neutralization shall be as complete as possible. 'Referring to Fig. 3,- it may be readily shown that the induction is completely neutralized both in magnitude and phase if,

.migen a and Uhr@ eg Tdt 2) Y 1 +--L Where These formulae show `that (with limitaw tions given later) it is readily possible to neutralize the induced alternating voltage correctly, since most of the values in the formulas may be controlled in the design of the system.

It was formerly customary to design transformers With a fixed value of p, then to' adjust the value of RL to suit. However, as shown later herein, it is desirable that RL be as low as economically practicable, and after considerable investigation I discovered that the number of primary turns must be adjusted accurately in order to obtain maximum efficiency. also found that it is not feasible to design a transformer with the correct number of `turns before installation, but the arrangement must be such that the number of turns can be accurately adjusted in the field. The procedure adopted is to construct the transformer With the primary coils in permanent form having t-he number of turns which is most likely to be used under various conditions7 and at the time of installation to add or subtract magnetically from the fixed turns by Winding additional turns over the coils, the added turns being connected in the primary circuit in a manner either to oppose or assist the fixed turns asV the case may require. The eXtra turns Wound over the fixed coils are indicated at X in miliare 'exposure to inductiom the value of induction is not ordinarily steady, but varies from time to time through Wide limits, at times becoming zero.) Moreover, the secondary coils of a transformer carry telegraph currents at various frequencies from zero up to the Working speed of the circuit. In addition, the primary circuit is liable to have stray direct currents flowing in it by conduction from neighboring` D. C. trolley systems, if there are any Within aA feW miles; this is especially likely to happen if RL is low (sec next section). The presence of telegraph currents in the secondaries, and the presence of stray direct currents in the primary coils, both tend partly to magnetize the core of the transformer, which tends to change the value of L. Any change in the value of L causes the neutralization of the induction to be less efficient. (See lEquation 4f.) (C is set at a final value at time of installation). These effects are all largely reduced by placing a suitable air gap in the magnetic circuit of the transformer. The air gap, of course, reduces the value of L; this is compensated for by increasing the value of C. lt is preferable that the gap be arranged so that at the time of installation it may be adjusted in length if desired, as this assists in obtaining the value of L which best suits the particular con ditions applying at a given transformer.

The effect of the air gap in the magnetic circuit is to increase the reluctance, maire it more constant throughout the range of flux densities used, and. to prevent saturation of the iron, thereby rendering the induction practically proportional to the inducing force. Due to the variable reluctance, and therefore the variable value of L, of a transformer having a closed iron magnetic circuit it has not heretofore been found practicable to use phase shifting devices for adjusting the phase of the neutralizing current, however, the transformer of my invention has practically a constant value of L and I am thereby enabled to use effectively a shunt condenser as a phase controlling device.V lt is obvious that the air gap might be formed by a single gap, or by tivo or more gaps at different partsof the magnetic core; or by employing a core made of iron dust or other divided magnetic materials, which provides multiple air gaps throughout the material. Referring to Fig. 2, F indicates the iron core of theneutralizing transformer which proper spaced relation by suitable clamping `means in 'order that the length of gaps G may be adjusted to the proper value. From Fig. 2 it vWill'be seen that the primary ofthe' transformer comprises several windings P sandwiched between secondary windings S at frequent intervals along the entire core, the primary windings being connected in parallel in the auxiliary circuit. vThe extra turns X are wound with heavy wire, and connected in series with regular turns P; all Varimary turns being'in parallel with cony denser C and directly in series with wire D;

The most severe limitation to the efficiency of a'transformer is the tendency of the transformer to cause crossfire, or interference between the various communication circuits carried through the secondary coils. Let it be assumed that one communication circuit is w carrying a current I of frequency r- Then it may be shown (neglecting It) that a voltage E .is induced in each of the other secondary coils, having the value Substituting the value or p as calculated from (3),this becomes I Esa-1 S R. Re RLS In the following table are given a series of values of E, for various values of RL. For this calculation the value of S has been taken at 1000; the value of RS at 2500, and the value of n at 20. These figures represent average conditions in practice. i

1o 9. ai

From the above it is apparent that the Crossfire can be very materially reduced by using a low value of primary wire resistance RL, preferably notmore than about 15 ohms. If the length of the exposure is say 20 miles, this requires a primary wire of conductivity equivalent to No. 1 B. & S. gauge. This condition represents a radical change from previous practice, in which it Was customary to use for the primary a circuit having from 50 to 100 ohms. y

It is readily apparentl that for given line conditions and a certain permissible value of E, the correct .value of the resistance RLk vof the auxiliary circuit may be determined from Equation (7) above.

Vhile I have described my invention in detail and worked out one specific example, it is for the purpose offexplanation and not by way of liinit-ation, and I do l'notintend to be limited as to details except as pointed out in the claims.

What I claim is:

l. In combination, two circuits located in a disturbing magnetic field, a transformer having its primary winding connected in one circuit and its secondary winding in the other, said transformer havinga magnetic circuit of substantially uniform reluctance whereby the induction is substantially proportional to the inducing current, and an adjustable condenser connected across one of said windings for adjusting the phase relation between the .disturbing voltage and the,

neutralizing voltage induced in one ofrsaid windings. f

V2. In combination, a plurality of commu- Y" nication circuits located in a disturbing magnetic field, an auxiliary circuit adjacentthe communication circuits, a transformer coupling said auxiliary circuit to the communication circuits whereby the disturbing voltages are neutralized` by voltages rinduced from the auxiliary circuit, vsaid auxiliary circuit having an abnormally low resistance as compared with the resistance of a communication circuit whereby cross-fire betweenthe communication circuits is substantially eliminated.

3. In a system for neutralizing disturbing voltages in a communication line in whichthe neutralizing voltages are induced into thel line from an auxiliary circuit by a neutralizing transformer having a condenser connected across one of its windings, the method of securing proper neutralization which consists in varying the ratio'of turns of the primary to the secondary to satisfy the equation and in varying the capacity of the condenser to satisfy the equation O'Lw2 1.

ing the eifcctire ratio of turns of the primary tothe secondary by .adding turns in series with the primary to as'" st or oppose the primary to satisfy the equation 5. In a system` for neutralizing disturbing voltages in communication lines in which the neutralizing voltages are induced into the lines from an auxiliary circuit by a neutralizing transformer, the method of securing proper neutralization and reducing the crossire between the lines to a permissible value E which consists in adjusting the constants of the elements of the system to satisfy the equa- 'tion I E nl S It, ZPL-HELE '6. In combination, in communication circuits, each circuit having a re"'stance one of said circuits carrying a current l, a auxiliary circuit, a transformer haring a primary winding connected in said auxiliary circuit and having an equivalent core less resistance S in said auxiliary circuit, and secondary windings connected in each of said communication circuits, said auxiliary circuit having a resistance RL of such value that the. voltage induced in adjacent communication circuits by the current I does not exceed a permissible value E, said resistance being deternlined from the equation *a* tm 7. In combination, two circuits located in a disturbing magnetic field, a transformer having its primary winding connected in one cir-- cuit and its secondary winding in the other, said transformer having a magnetic circuit of substantially uniform reluctance.

8. In combination, two circuits located in a disturbing magnetic field, a transformer having a winding connected'in each circuit, said transformer `having a core of magnetic material with one or more air gaps in the magnetic circuit, and an adjustable condenser connected across one or more of said windings for adjusting the phase relation of the neutralizing if'oltageand disturbing voltage.

9. ln combination, a plurality of communication circuits located in a disturbing magnctic field, an auxiliary circuit adjacent to the communicationl circuit-s, a transformer haring a core of substantiallyl uniform reluctance and having a plurality of windings, one winding connected in each of said circuits, and a condenser or condensers connected across one or more of said windings whereby the phase relation of the neutralizing voltage and disturbing voltage may be adjusted.

l0. ln combination,v a plurality of communication circuits located in a disturbing magnetic licld,an auxiliary circuit adjacent to the communication circuits, said auxiliary circuit having an abnormally low resistance compared with the resistance of the communication circuits whereby the creation of cross-lire among the communication circuits is substantially avoided, a transformer coupling said auxiliary circuit to the communication circuits, said transformer having a magnetic circuit of substantially uniform reluctance whereby the neutralizing voltage in the communication circuits is substantially proportional to the inducing current in said transformer.

i In testimony whereof l alliX my signature.

JOSEPH W. MILNGR. 

